Soil and groundwater contamination with man-made products presents a serious problem. Environmental contaminants must be managed to protect human health and the environment, and to restore aquifers to productive use. Typical groundwater contaminants include chlorinated halogenated straight-chain and aromatic hydrocarbons, perchlorate explosive materials such as aromatic nitrates, residues of energetic munitions, nitrates, acids, radionuclides and metal oxides.
Remediation of groundwater containing such contaminants can be effected using anaerobic bio-degradation processes in low permeability, saturated or variably saturated soils at a substantially lower cost than conventional methods. Anaerobic reducing conditions can be created by the addition of an organic substrate to an aquifer. The organic material initially consumes any oxygen or other electron acceptors such as nitrates (NO3) or sulfates (SO4), and then provides a carbon source and an electron donor for reductive chlorination. Interest has grown in the use of slow release electron donors in enhanced bioremediation (also referred to as biostimulation) systems for treating contaminants in groundwater. Emulsified vegetable oils have been used as carbon sources for enhanced halorespiration, which is the use of halogenated compounds as sources of energy. Halorespiration is also known as dehalorespiration and is a major form of anaerobic respiration which can play a part in microbial trichloroethene biodegradation. Common contaminants include chlorinated aliphatic compounds such as perchloroethene (PCE) and trichloroethene (TCE) and chlorinated phenols. Trichloroethene is the most common contaminant in groundwater.
Currently available electron donor compositions include emulsified vegetable oil (EVO) containing 25 to 50% water. These emulsified vegetable oils are inherently unstable and, thus, emulsions do not tend to form spontaneously. Energy input such as shaking, stirring or homogenizing is needed to form an emulsion. The compositions generally have a mean droplet size of one micron or greater. Over time, emulsions tend to revert to the stable state of the phases comprising the emulsion. The composition is purchased from a supplier and shipped to a contamination site. Typical dilution ratios range from one part EVO to four parts water to one part EVO to twenty parts water. Additional chase water is often added to aid with distribution. The cost of the electron donor may be a significant portion of the total process cost. The choosing of an efficient and low cost electron donor is important to the efficacy and overall economics of the bioremediation process.
Emulsions contain both a dispersed and a continuous phase. The boundary between the phases is called the interface. EVO composition providers with oil as the dispersed phase and water as the continuous phase include EOS Remediation, LLC, RNAS, Inc., and Terra Systems Inc./HePURE Technologies. The main ingredients of the products offered by the companies include, by weight, 45 to 60 percent refined, bleached and deodorized soybean oil, less than 10 percent food additives, emulsifiers, preservatives such as lethicin and 4 percent of a soluble substrate such as sodium or potassium lactate or lactic acid, with the balance being water.
A JRW composition (see U.S. Pat. No. 7,785,468) is a soy-based water in oil substrate. Water is the dispersed phase and oil as the continuous phase. The main ingredients of the composition are 45 percent soy-based oleaginous material, 35 percent ethyl acetate and 20 percent water. Other patents describing EVO compositions include U.S. Pat. No. 5,265,674 (Fredrickson et al), U.S. RE 40,448 and RE 40,734 (Borden et al) and U.S. Pat. No. 6,806,078 (Newman).